Theoretical Study On The Structure And Optical Properties Of Si Nanoparticles And CuSCN

As nanotechnology developed rapidly, all kinds of nanomaterials came forward in great numbers. The excellent characteristic and special function of nanomaterials made it have a broad application prospect.This thesis included two parts:In part one, Using the discrete dipole approximation method, the optical properties of Si spherical nanoparticles in different size were calculated. The effective radius of these particles ranged from10nm to100nm. As the particle effective radius increased, the calculated peak position of the absorption efficiency spectrum, scattering efficiency spectrum and extinction efficiency spectrum appeared red shift. And the shape of the curves about the absorption efficiency, scattering efficiency and extinction efficiency spectrum was also changed. New absorption, scattering and extinction efficiency peak emerged. Secondly, the electric field distribution in particle interior and surface under incident radiation were calculated. The results showed that the spread of the electric field inside the particle was highly affected by the particle size and the polarization of the incident radiation. In addition, the influence of the ambient medium on the optical properties of Si nanoparticles were also studied. Here, the refractive index of the ambient medium was set to1.33. And the extinction efficiency spectrum of Si nanoparticles, of which the effective radius ranged from5nm to80nm, were calculated respectively. The relation between the peak position of the extinction efficiency factor and the effective radius of the nanoparticles was analysed. Besides the effective radius of nanoparticles, The shape of the particles also had a great influence on its optical properties. In this thesis, the extinction efficiency factor of two kinds of cylinders of which the height were100nm and150nm was calculated separately. The cross section diameter of the cylinders changed from10nm to100nm. The diagrams were made separately to show the relation between the peak position of extinction efficiency spectrum and cross section diameter of the two kinds of cylinders. These results showed that the optical properties of cylindrical Si nanoparticles were greatly affected by the cylindrical aspect ratio. At last, the optical properties of infinite array of cylindrical Si nanoparticles were calculated in this section. The absorption, scattering, and extinction efficiency factor of the array with different cylindrical aspect ratio were analysed. And the diagrams of electric field distribution inside the particles under the incident irradiation were given.In part two, β-CuSCN is a kind of important p-type semiconductor material. It’s widely used in dye-sensitized solar cells and extremely thin absorber solar cells. Using the first principle method based on density functional theory, the band structure and optical properties of β-CuSCN crystal with or without Cu vacancies were studied in this thesis. The models built here were the8-site CuSCN primitive cell, the32-site supercell (2×2×1of primitive cell) with a Cu vacancy, and the72-site supercell (3×3×1of primitive cell) with a Cu vacancy. It showed that β-CuSCN was an indirect band-gap semiconductor, and its band-gap is2.03eV. Removing a Cu atom from the32-site supercell lead to changes in band structure. The conductor band moved upward and the band-gap become wide. Two accepter levels above the Fermi level were observed in the32-site supercell with a Cu vacancy, which resulted in the onset of a small absorption pre-peak at0.65eV. Such a phenomenon was not observed in the band structure and the optical absorption spectrum of72-site supercell with a Cu vacancy.